The present invention relates to an image-taking apparatus which drives a mirror which can move into and out of an image-taking optical path.
A mirror drive mechanism of a single-lens reflex camera has a motor, a mirror drive cam gear having a cam portion, a mirror drive lever which drives the rotation of a movable mirror by the lift of the cam portion of the mirror drive cam gear, a shutter drive cam gear having a cam portion, and a shutter drive lever which charges and drives a shutter by the lift of the cam portion of the shutter drive cam gear (for example, see Japanese Patent Publication No. 7-27156).
In the drive mechanism, the mirror drive cam gear directly engages with the shutter drive cam gear, and a transmission gear for transmitting the torque of the motor in one direction engages with one of the cam gears.
The mirror drive cam gear, the shutter drive cam gear, and the transmission gear which engages with one of the cam gears are arranged such that they engage with each other in series. Thus, from the viewpoint of the other cam gear, the number of gear stages through which the motor driving force is transmitted is increased by one as compared with the one cam gear, so that the drive efficiency is not favorable.
In addition, since the mirror drive cam gear directly engages with the shutter drive cam gear, the cam gears rotate in opposite directions. This prevents an ideal arrangement of the rotational axes of the mirror drive lever and the shutter drive lever in view of the drive efficiency.
The mirror drive cam gear directly engages with the shutter drive cam gear and they occupy a pear-shaped space when viewed in the directions of the rotational axes of the cam gears. It is thus impossible to place the mirror drive lever and the shutter drive lever in an ideal arrangement in view of their respective drive efficiencies, which is disadvantageous in the drive efficiency and may increase the size of the camera.
To address them, a drive mechanism has been disclosed in which a mirror transmission gear engaging with a mirror drive cam gear and a shutter transmission gear engaging with a shutter drive cam gear are disposed coaxially and a transmission gear shaft driven by a motor is provided (for example, Japanese Patent Laid-Open No. 2002-23221). According to the abovementioned structure, since the driving force of the motor is directly transmitted to the mirror drive cam gear and the shutter drive cam gear from the associated transmission gears, the difference in drive efficiency caused by the number of gear stages can be reduced as compared with the structure in which the transmission gear engages only with the one of cam gears which engages with the other cam gear. In addition, the mirror drive cam gear and the shutter drive cam gear can be rotated in the same direction to achieve an ideal arrangement of the rotation axes of a mirror drive lever and a shutter drive lever in view of the drive efficiency.
In the abovementioned mechanism, however, the number of parts is increased, and a phase shift may occur in the mirror drive cam gear and the shutter drive cam gear in assembly operation. Also, since the mirror drive cam gear and the shutter drive cam gear are coupled through the transmission gears, the backlash of the gears causes a phase shift, and the rotation of one of the cam gears is feedback controlled, the interlocking drive of a mirror and a shutter cannot be performed with high accuracy.
In the abovementioned two drive mechanisms, when the mirror is moved from within an image-taking optical path to the outside thereof, or when the mirror is moved into the image-taking optical path from the outside thereof, the mirror is driven by the lift of the cam, so that the mirror drive time is extended due to a change in voltage or the like.
Japanese Patent Laid-Open No. 1-134443 has disclosed a mirror drive mechanism which drives a mirror at high speed. The mirror drive mechanism is formed of a first engaging portion which positions the mirror in an image-taking optical path, a first spring which urges the mirror in a direction in which the mirror is moved out of the image-taking optical path, a second engaging portion which positions the mirror outside the image-taking optical path, and a second spring which urges the mirror in a direction in which the mirror is moved into the image-taking optical path, an electromagnet which releases the engagement in the first and second engaging portions, and a motor which charges the first and second springs.
While the mirror drive mechanism allows the high-speed drive of the mirror, it needs a plurality of driving sources and a number of the constituent parts, requiring extremely high cost. In addition, the electromagnet has a finite releasing action on the engagement in the engagement portions and the positioning of the engagement portions cannot be enhanced.
Another image-taking apparatus has been disclosed which has a mirror drive mechanism which utilizes the biasing force of a charged drive spring to allow a mirror to move into and out of an image-taking optical path and requires only one motor as a drive source (Japanese Patent Laid-Open No. 2002-174850).
In the abovementioned mechanism, the engagement of a raising lever needs to be released when the mirror is driven into the image-taking optical path from the outside thereof. Driving the motor for the engagement release simultaneously causes the charging of the spring for biasing the mirror toward the outside of the image-taking optical path, thereby increasing the load on the motor to take a long time for the engagement release.
The motor is rotated in different directions when the mirror is moved out of the image-taking optical path and when the mirror is moved into the image-taking optical path. Since a mechanical lock is used to forcedly stop a cam gear in order to stop the rotation of the motor, a higher mechanical load is applied.
Another mirror drive mechanism drives a charge lever by a cam gear after the completion of mirror drive operation to position an engaging portion of a hold lever provided for the charge lever to a claw portion of a mirror lever. In the mechanism, however, the charge lever is driven at high speed when the engaging portion of the hold lever is positioned to the claw portion of the mirror lever, so that the end of the hold lever at high speed collides with the claw portion of the mirror lever. This may reduce the durability of the end of the hold lever and the claw portion of the mirror lever.
As a means for solving this, Japanese Patent Laid-Open No. 1-134443 mentioned above has disclosed the structure in which the end of the hold lever is always in contact with the claw portion of the mirror lever to avoid a collision between the end of the hold lever and the claw portion of the mirror lever.
In the mechanism, however, the end of the hold lever is always in slide contact with the claw portion of the mirror lever, so that the end of the hold lever needs to extend longer than the charge stroke of the charge lever to cause an increased size of the camera.